The temporomandibular joint (jawbone joint, or TMJ for short) is a modified hinge joint connecting the condylar head of the mandible to the temporal bone of the skull. Opening and closing the mouth or jaw is a combination of translatory (i.e., gliding) and rotational movements of the condylar head along the temporal bone. Translation of the condylar head produces protrusion (protraction) of the chin and retrusion (retraction) of the chin. Rotation of the condylar head produces depression and elevation of the mandible. The primary muscle involved in protrusion is the lateral pterygoid muscle. The primary muscle responsible for retrusion is the temporal muscle with minimal, secondary involvement of the masseter muscle. Along with gravity, the muscles responsible for depression or opening the jaw are the lateral pterygoid muscle and the small, strap like muscles located at the front of the neck called the supra and infra hyoid muscles. The primary muscles responsible for elevation or closing the jaw and opposing the hyoid muscle group are the larger and more dominating temporal, masseter and medial pterygoid muscles located at the sides of the skull and jaw.
The temporal, masseter and medial pterygoid muscles that close the mouth work almost constantly in such activities as chewing, talking, and stressful clenching. As a result, these muscles can become overly strengthened and shortened with respect to the supra hyoid, infra hyoid and lateral pterygoid muscles that open the mouth. This creates an imbalance at the TMJ. Poor alignment of the head and neck worsens this imbalance, and both the TMJ imbalance and the neck musculature imbalance may perpetuate each other's dysfunction. Such imbalance results in discomfort and pain that can lead to tinnitus, vertigo, headache, vision problems, difficulties in chewing and talking, and pain in the upper back and shoulders. This condition is known as TMJ dysfunction (TMD). TMD can be self-perpetuating in that the muscles that close the mouth go into spasms, resulting in more clenching that aggravates the condition.
Physical therapy and rehabilitation using exercise are based on restoring normal function and balance within the musculoskeletal system. Each skeletal muscle or agonist has at least one opposing or antagonistic muscle with which it interacts. The proportional strength ratio of antagonistic to agonist muscle pairs must be in balance for muscles to function normally. Imbalances can occur from inactivity, overuse, disease, malnutrition and direct trauma resulting in injury. To restore balance, a therapist must identify the muscles that have become dysfunctional and determine which ones are weak versus those of their antagonists that have become over dominating. By designing an exercise regime that strengthens the weak muscles and therefore lessens the influence of the over dominating muscles, balance is restored and normal, pain free function is re-established.
Therapeutic exercises for restoring normal function to target muscles and the joints they act upon stimulate (activate) target muscles and in turn stretch their antagonistic partners. Therapeutic exercise for TMD is designed to stimulate the muscles that open and protrude the jaw and in turn stretch the antagonistic muscles that close and retract the jaw. The muscles and the joint they act upon should be exercised through their full functional range of motion. Therefore, the exercise should ensure the rotational and translatory motion aspects of the TMJ throughout the applied resistance.
Patients with TMD are often instructed to apply their hand or fist to their chin to generate resistance against opening and protracting the jaw. This strengthens the lateral pterygoid and hyoid muscles, alleviating the imbalance at the TMJ. However, applying resistance in this manner creates counterproductive tension in the musculature of the arms, shoulders or neck and induces poor head position. This tension limits the effectiveness of the exercise.
A variety of devices generally fitting the head and neck have been described. U.S. Publication 2006/0,106,330 to Andrade et al. depicts a facial toning device. U.S. Pat. No. 4,694,823 to Young shows a neck and facial lifter. Anti-apnea appliances are described in U.S. Pat. No. 5,893,365 to Anderson; U.S. Pat. No. 7,225,811 to Ruiz et al.; U.S. Publication 2007/0,181,135 to Baker; and U.S. Pat. No. D550,849 to Baker. U.S. Pat. No. 5,484,359 to Wabafiyebazu shows a full-face enclosure for toning chin muscles. An orthodontal device is shown in U.S. Pat. No. 7,121,824 to Keles et al. A device for tensioning the TMJ as treatment for a dislocated jaw is shown in U.S. Pat. No. 6,016,807 to Lodge. U.S. Pat. No. 1,587,558 to Sheffield illustrates a jaw bracing and setting device with a fixed angle between a chin strap and a head strap assembly. A jaw exercising device also with a fixed angle between chin strap and headband is disclosed in U.S. Pat. No. 4,650,182 to Ross.
There remains a need for a way to strengthen the lateral pterygoid and hyoid muscles so as to alleviate TMD without undesirable effects on musculature elsewhere in the human body.